The present invention relates to an internal combustion engine crankcase gas flow rate control assembly and system and, more particularly, to a positive crankcase ventilation (“PCV”) gas flow rate control assembly and system for controlling the recirculation of gas discharge from an engine in accordance with engine operating conditions and also in accordance with flow rate adjustments made to the gas flow rate control system.
A PCV system provides a controlled mechanism for gases to escape the crankcase of an internal combustion engine. The heart of this system is the PCV valve, typically a single channel variable-restriction valve that can react to changing pressure values and intermittently vary flow rates while allowing the passage of the gases to their intended destination. In most modern vehicles the intended destination is the engine's intake stream.
Internal combustion inevitably involves a small but continual amount of blow-by gases, which will occur when some of the gases from the combustion leak past the piston rings to end up inside the crankcase. The gases could be vented through a simple hole or tube directly to the atmosphere, or they could “find their own way out” past baffles or past the oil seals of shafts or the gaskets of bolted joints. This is not a problem from a mechanical engineering viewpoint alone; but from other viewpoints, such as cleanliness for the user and environmental protection, such simple ventilation methods are not enough; escape of oil and gases must be prevented via a closed system that routes the escaping gases to the engine's intake stream and allows fresh air to be introduced into the crankcase for better and more efficient combustion.
From late in the 19th century through the early 20th century, blow-by gases were allowed to find their own way out past seals and gaskets in automotive vehicles. It was considered normal for oil to be found both inside and outside an engine, and for oil to drip to the ground in small but constant amounts. Bearing and valve designs generally made little to no provision for keeping oil or waste gases contained. In internal combustion engines, the hydrocarbon-rich blow-by gases would diffuse through the oil in the seals and gaskets into the atmosphere. Engines with high amounts of blow-by would leak profusely.
Until the early 1960s, automotive engines vented combustion gases directly to the atmosphere through a simple vent tube. Frequently, this consisted of a pipe (the ‘road draft tube’) that extended out from the crankcase down to the bottom of the engine compartment. The bottom of the pipe was open to the atmosphere, and was placed such that when the car was in motion a slight vacuum was obtained, helping to extract combustion gases as they collected in the crankcase. Oil mist would also be discharged, resulting in an oily film being deposited in the middle of each travel lane on heavily-used roads. The system was not “positive”, as gases could travel both ways, or not move at all, depending on conditions.
Environmental concerns lead to the development of controlling combustion gases in an engine. The PCV valve and system operates as a variable and calibrated air leak whereby the engine returns its crankcase combustion gases. Instead of the gases being vented to the atmosphere, these gases are fed back into the intake manifold, re-entering the combustion chamber as part of a fresh charge of air and fuel. All the air collected by the air cleaner (and metered by the mass flow sensor, on a fuel injected engine) goes through the intake manifold. The PCV system diverts a small percentage of this air via the breather to the crankcase before allowing it to be drawn back into the intake tract again. The positive crankcase ventilation system is an “open system” in that fresh exterior air is continuously used to flush contaminants from the crankcase and draw them into the combustion chamber.
FIGS. 1A-1D illustrate a typical PCV system's use in an internal combustion engine. As illustrated in FIG. 1A and as described in U.S. Pat. No. 5,027,784, an internal combustion engine includes a cylinder head 1, a cylinder head cover 2, a cylinder block 3, and an oil pan 4. A typical prior art PCV system includes a PCV “vacuum” connection line 7 connecting the cylinder head cover 2 to a portion of an intake passage 8 of the internal combustion engine at a location downstream of a throttle valve 9. A PCV valve 6 is provided for controlling flow of blow-by gas in the PCV connection line 7. A baffle plate 12 provided in the cylinder head cover 2 acts as a primary trap for oil mist contained in the blow-by gas. A trap chamber 5 on the downstream or vacuum side of the PCV valve 6 serves as a secondary trap for oil mist in the blow-by gas. Oil mist trapped in the trap chamber 5 collects on a bottom wall 5′ of the trap chamber 5.
During engine operation, blow-by gas which has leaked past a piston into a crankcase of the cylinder block 3, flows into the cylinder head cover 2 through a path formed in the cylinder block 3 and the cylinder head 1. The blow-by gas, controlled by the PCV valve 6, then flows through the PCV connection line 7 into the intake passage 8 of the engine to be burned in the combustion chamber.
The PCV system of FIG. 1A relies on the fact that, while the engine is running under light load and moderate throttle opening, the intake manifold's pressure is always less than crankcase pressure. The lower pressure of the intake manifold draws gases towards it, pulling air from the breather through the crankcase where the air is diluted and mixed with combustion gases through the PCV valve, and returned to the intake manifold. Typical PCV system PCV connection tubes (e.g., 7) connect the crankcase to a clean source of fresh air, namely, the air cleaner body. Usually, clean air from the air cleaner flows into this tube and into the engine after passing through a screen, baffle, or other simple system to arrest a flame front in order to prevent a potentially explosive atmosphere within the engine crankcase from being ignited from a backfire into the intake manifold. Once inside the engine, the air circulates around the interior of the engine, picking up and clearing away combustion byproduct gases, including any substantive amounts of water vapor which includes dissolved chemical combustion byproducts. The combined gases then exit through another simple baffle, screen, or mesh to trap oil droplets before being drawn out through the PCV valve 6 and into the intake manifold 8.
The typical PCV valve 6 is a simple mechanism with a few moving parts, as illustrated in FIGS. 1B, 1C, and 1D, but it performs a somewhat complicated gas flow control function. In some prior art PCV valve assemblies, an internal restrictor 13 (generally a piston or pintle) is held in “normal” (engine off, zero vacuum) position with a light spring 14, exposing the full size of the PCV opening to the intake manifold. With the engine running, the pintle is drawn towards the manifold side in the PCV valve by manifold vacuum, restricting the opening proportionate to the level of engine vacuum vs. spring force. At idle, the intake manifold vacuum is near maximum (as best seen in FIG. 1B). It is at this time the least amount of blow-by is actually occurring, so the PCV valve provides a large amount of (but not complete) restriction. As engine load increases, vacuum on the valve decreases proportionally and blow by increases proportionally. With a lower level of vacuum, the spring 14 returns the pintle 13 to the “open” position to allow more air flow. At full throttle (see, e.g., FIG. 1C), vacuum is much reduced, down to between 1.5 and 3 inches of Hg. At this point the PCV valve is essentially open and flowing, and most combustion gases escape via the “breather tube” where they are then drawn into the engine's intake manifold. Should the intake manifold's pressure be higher than that of the crankcase (which can happen in a turbocharged engine, or under certain conditions of use, such as an intake backfire, see, e.g., FIG. 1D), the PCV valve closes to prevent backflow into the crankcase.
In prior art PCV systems, the parts of the PCV system should be kept clean and open, otherwise air flow may be insufficient. A malfunctioning PCV valve may eventually damage an engine. Typical maintenance schedules for gasoline engines include PCV valve replacement whenever the air filter or spark plugs are replaced, because anything with moving parts inside may eventually fail.
Most gasoline powered internal combustion engines utilize PCV valves. The basic design of the PCV valve (as illustrated in FIGS. 1A-1D) has not changed much since its first introduction in passenger vehicles. The operating characteristics that define a PCV valve are: idle flow rate; cruise flow rate; transition vacuum level, and backfire-backflow prevention. Idle flow rate is the determination of the quantity of gas flowing through the PCV valve during high vacuum conditions existing when an engine is idling (See FIG. 1B). Cruise flow rate is the determination of the quantity of gas flowing through the PCV valve during low vacuum conditions when the engine is operating at higher rpm's during, for example, vehicle acceleration (See FIG. 1C). Transition vacuum level is the vacuum level at which the PCV valve switches from a low to a high flow rate, and backfire-backflow prevention is required in those rare situations where manifold pressure exceeds crankcase pressure (See FIG. 1D). A properly operating PCV valve should exhibit a decreasing flow curve with increasing vacuum, but a malfunctioning PCV valve can result in crankcase over pressure, oil sludge, oil leaks, poor fuel economy, rough idle and other problems.
In order to achieve the desired decreasing flow curve, most PCV valves employ a spring-pintle design as shown in FIGS. 1B-1D, and as a result, in most PCV valve designs, the flow passage is a variable annular area, which varies as the pintle moves linearly. The open lumen area defined by this annular opening can be as small as 0.25-0.3 mm and, in operation, the PCV valve assembly is prone to blockage from clogging. In addition, typical PCV valves such as those shown in FIGS. 1A-1D which have a spring/pintle assembly are also prone to sticking in one position or another.
Certain kinds of engines present additional problems. For example, engines with superchargers or turbochargers require intake manifold structures which are more complicated. As illustrated in FIG. 1A, the typical PCV design includes a tube from upstream of the throttle body to the crankcase, and a tube from the crankcase to the intake manifold that includes a PCV valve. The PCV system is designed to work on intake manifold vacuum, which is available in most operating conditions of a Naturally Aspirated (NA) engine. Automotive manufacturers are beginning to transition from larger NA engines to smaller Turbo Charged engines for improved fuel efficiency. The switch to turbo engines has created a need for different PCV system configurations.
Prior art PCV systems for use with Turbo Charge engines typically include a second PCV assembly which includes a flapper valve over a larger orifice for the boosted flow and a small orifice for the non-boosted flow, but problematic flapper valve members can get stuck (e.g., in a closed state), and, like typical PCV valves such as those shown in FIGS. 1B-1D, run a risk of clogging.
It is an object of the present invention to overcome these problems and provide an improved, more durable and trouble-free PCV valve for use in an improved PCV system which will minimize the likelihood of sticking or clogging problems and enhance long term engine performance.